We abhor them and only their sight can make us sick. But they represent one of the oldest human companions, that's why the DNA of the Black Rat (Rattus rattus) has proved to be useful in explaining how ancient people and diseases spread together with the ancient black rats. Today, this rat is spread all around the world; it was brought involuntarily by humans, but the species appeared in Eastern/Southern Asia.
The new study presented at the Archaeological Science Conference in Canberra, Australia, investigated the mitochondrial DNA of 165 Black Rat individuals coming from 32 countries around the world. Analyzing the species' gene pool, 6 different lineages were detected, each one coming from a different area of Asia.
"Black Rats are carriers of many different human diseases, including
plague, typhus and leptospirosis. It has been unclear why certain rodent-borne diseases are more common in some places than others, but our work raises the possibility that the different lineages of Black Rats each carry a different set of diseases, which is something medical science now needs to consider. We need to know more about what types of Black Rats are moving around the world and what disease risks each of them might pose," said lead author Dr Ken Aplin, CSIRO mammal expert.
The 6 lineages appeared in India, Taiwan, the Himalayas, Thailand, the Mekong Delta, and Indonesia.
The Indian race spread to the Middle-East around 20,000 years ago, and from this area it spread to Europe. Human voyages during the recent centuries transported this rat to Africa, the Americas and Australia.
The Taiwan breed moved to Japan, the Philippines, and Indonesia, reaching Micronesia 3,500 years ago. The other 4 lineages are not so widespread.
"Our findings also show a good match between the historic spread of each lineage and ancient routes of human migration and trade, but there are a few surprises that raise new questions about human prehistory. The genetic evidence points strongly to there being more than one species of black rat, but more work is needed before we can say exactly how many species there are," said Aplin.
The Black Rat belongs to one of the largest rodent genus, Rattus, with 56 species, whose original area is in Eastern/Southern Asia and New Guinea. The other common human-associated species is the Brown Rat (Rattus norvegicus), originated in China. This species eliminates the Black Rat if the two are in the same region. Other species are human associated, but with a more restricted distribution, like the Polynesian Rat (Rattus exulans),
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